The major goals of the research proposed in this application are to gain understanding of the functions of the viral gene products required for and controlling viral transformation and replication. The specific aims to be pursued are: 1) to characterize recently isolated mutants with deletions in either E1A or E1B in order to investigate the gene products required for cell transformation and regulatory interactions between viral transcription units; 2) to develop a general method of gene-directed mutagenesis in order to select from each of the early transcription regions a number of conditionally lethal, temperature-sensitive (ts) mutants to permit functional studies of the gene products regulating replication and transformation; and 3) to investigate the early viral and cellular DNA interactions leading to transformation using a) newly developed rat cell line which transforms at a relatively high frequency, and b) selected mutants which transform at either high or low frequency.